I had the same problem with my MY 2008 3.0 i took delivery of in October 2007. After 6 months of dealing with BMW USA and almost getting a new vehicle, they traced the problem to a bad cylinder head. At some point they discovered the problem and switched to a re-designed head. My vehicle was supposed to have the new head (according to my VIN), but when they took the head off, it was the old one. They replaced it and solved the problem. No noise since then! My vehicle was in the shop about ten times for a total of more than 3 months time during a 6 month period to resolve this. The bleeding proceedure would only last a couple of weeks and they did that 3 times. It got to the point where them service manager gave my vehicle to one of the service guys to drive for a week to try and replicate the problem. Then once they confirmed there was a problem, they had to make several conference calls to Germany with the engine design team to try and figure it out. When they replaced the head finally, it was the last attempt BMW was going to make to fix it before they gave me a new X6 to replace my X5.